1. Field of the Invention
The present invention relates to a photodetector device for detecting the presence of a moving body such as sheet or the length of a moving sheet with respect to the direction in which the moving sheet is moved, by means of an output, based on variations in the quantity of light, from a photoelectric means provided in the vicinity of a path of a moving sheet and, more particularly, to a photodetector device suitably used for detecting a moving sheet, especially, a moving original in an automatic original feed unit in a copying machine, from an output based on variations in the quantity of light and varying greatly due to external factors.
2. Description of the Prior Art
An automatic original feed unit is capable or automatically feeding an original to be copied, through an operation of a copying button. In this automatic original feeding operation, originals stacked on a supplying tray are automatically transferred one by one to a copying position or onto a copy board, and originals which have been copied are automatically discharged onto a collecting tray.
Although FIG. 1 is a schematic illustration of an automatic original feed unit according to the present invention, for the convenience of description of the construction or arrangement relation to the unit it is used as a conventional automatic original feed unit. Referring to FIG. 1, a copying machine body 1 is provided with an automatic original feed unit 2 which is integrally formed with a copy board 10 thereof. This original feed unit 2 consists of a main body 3, and a movable body 5 pivotally supported on a shaft 4 in the main body 3 such that the movable body 5 can be moved in the vertical direction on the copy board. The main body 3 is provided with an original feed table 7 onto which one or a plurality of originals are inserted from a chute 6 a feeding roller 8 driven by an original feeding instruction to feed an original from the feed table 7, and a carrying roller 9 driven in the same manner at the same peripheral speed as the feeding roller 8 to transfer the original towards the side of the movable body 5.
A supplying tray mentioned above is same meaning with a unit consisting of the chute 6 and the original feed table 7. Therefore, the unit is called as supplying device, sometimes.
The movable body 5 is provided with a transfer device consisting of a conveyor belt 11, pulleys 12, 13, idlers 14, 15, 16, a guide roller 17 and a discharge roller 18, so as to transfer an original which has been fed from the carrying roller 9 and which is placed on the copy board made of glass to a proper position, and discharge the original on the copy board 10 at the completion of a copying operation therefor.
The pulley 12 (or 13) is driven by a motor (not shown) directly or via an electromagnetic clutch when an original is fed or when an original is discharged.
The movable body 5 is provided in addition to the above-mentioned members with a stopper 19 which is projected on the surface of and at the front side of the copy board 10 by a plunger action so as to stop the original to a proper position during the transfer thereof.
Reference numeral 20 denotes a guide member adapted to guide the original from the guide roller 17 to the discharge roller 18 during an original discharging operation, 21 a discharge port, and 22 a collecting tray serving also as a cover for the movable body 5.
In an automatic original feed unit described above, it is necessary to stop an original fed from an original supplying tray, when the original has been transferred to a proper position (the stopper 19) on the glass forming a copy board 10, namely, to stop the movement of the conveyor belt 11 in accordance with the copying operation. When the conveyor belt 11 is not stopped accurately, originals may be jammed at the position providing the stopper 19 or originals may not be stopped in a proper copying position. Therefore, it is to be desired that the movement of the conveyor belt 11 be controlled, properly, in consideration of the inertia force of the transfer device based on the motor mentioned above.
In order to properly stop the original, it is necessary to provide a sensor or detecting means for sensing the arrival of the original at a predetermined position.
Methods conceivable of stopping the original in a proper position include a one employing a sensor disposed immediately before the stopper 19 to stop the original in which the motor for transfer device is sheet off of the operation at a moment when the front end or edge of the original is sensed by the sensor, and a one employing a sensor disposed in the space in the path of original which is between the carrying roller 9 and the conveyor belt to determine the original stopping point on the basis of time defined by a distance between the point at which the sensor is disposed and the given original stopping position and the transfer speed of the original.
In the latter method, a sensor of a simple construction may be used, which consists of a light receiving element and a luminescent element disposed on both sides of the path of the original. However, this method is very unstable, namely, originals often slip on the conveyor belt and the transfer speed of originals tends to fluctuate. Consequently, it is difficult to stop the original at a high accuracy by this method.
On the other hand, the former method easily attains a high accuracy of detecting and stopping the original. The sensor employed in this method is placed on the copy board 10, in general, in a copying machine. Therefore, if the above-mentioned light-permeating sensor is utilized in this method, it becomes necessary to dispose, for example, a light receiving element within the copying machine body and a luminescent element on the side of the automatic original feed unit so as to set opposite to each other. This causes a restriction on the designing of the automatic original feed unit. Namely, it is very inconvenient to separately form an automatic original feed unit such that the feed unit can be detachably set in a copying machine.
Therefore, a method employing a reflector type sensor as schematically shown in FIG. 2 is preferably used, in which a sensor consists of a luminescent element 23 and a light receiving element 24 is set in a holder 25 and disposed on the side of the automatic original feed unit. In other words, the two elements are disposed on the same side to the passage of the moving body. In this method, an optical output from the luminescent element 23 is reflected on the glass forming a copy board 10, so as to be guided to the light receiving element 24.
However, since this reflector type sensor utilizes the light reflected on the glass constituting a copy board or the light reflected on the original, it has a low utilization rate of light, a low level of output from the light receiving element, a large temperature drift in the output from the light receiving element due to the radiation of heat from an exposure lamp for exposing the original to be copied a considerable variations in reflection factor due to stains on the glass constituting a copy board, a considerable distribution in the sensitivity of the light receiving element itself, and a slight slippage in the optical axes. Accordingly, the detection accuracy of the above sensor is extremely low.
Such problems due to the environmental factors are also raised in a case where a light-permeating sensor is used in an atmosphere having various kinds of external disturbances, for example, an environment which has influence on the irradiation of light on the path of originals.